Tamper proof lock



Nov. 19, 1963 R. w. MAYNARD 3,111,022

TAMPER PROOF LOCK Orlginal Filed April 27, 1960 2 Sheets-Sheet 1 I'l'wm INVENT OR.

Nov. 19, 1963 R. w. MAYNARD 3,111,022

TAMPER PROOF LOCK Orlginal Filed April 27, 1960 2 Sheets-Sheet 2 `|OS` 10G` 5 104-` 7 41 44 1of\/// T-.7501.5

INVENTOR.

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United States Patent O il n 3,l11,022 TAMPER PROF LOCK Robert W. Maynard, Cincinnati, hio, assigner to The lviosler Sete Co., Hamilton, Ghia, a corporation oi New York @riginal application Apr. 27, i966, Ser. No. 25,074. Divided and this application Mar. 2d, lll, der. No.

iosgsaz s erstma. (ci. rit-33s) This invention is directed to a lock having improved means for protection against attack by means of the application of heat or by removal of the cover plate of the lock mechanism. The invention is primarily intended for use with combination locks, although it may be used with other types of locks.

This application is a division of my co-pending application Serial No. 25,074, filed April 27, 1960, entitled Tamper Proof Combination Lock.

One rather frequently used method for surreptitiously attacking a lock involves moderate heating of the lock which, even short of melting or permanently damaging the lock mechanism, can enable someone with sufficient skill to open the lock without setting the combination.

A principal objective of this invention is the provision of a lock in which the bolt is automatically and positively pinned against opening when heat is applied to the lock.

Another objective of the invention is the provision of means whereby the bolt is prevented from being drawn in upon the forcible removal of the cover plate of the lock.

Simply put, this invention contemplates a lock having a case and a bolt slidable between lock and unlock positions with respect to the case, a movable pin urged toward pinning engagement with the bolt when the bolt is in lock position, and meltable means normally restraining the pin from engaging the bolt but which will melt at a relatively low temperature it heat is applied to the lock to release or remove the restrain on the pin, whereby the pin will then pin the bolt against movement from lock position. Preferably the meltable pin restraining means are mounted on a cover plate secured to the lock case, so that if the cover plate is forcibly removed from the case, as by being knocked away, the pin will be released and will pin the bolt in lock position, even in the absence of the application of heat.

Further objectives and advantages of the invention can best be made apparent by reference to the following detailed description ot the drawings in which a preferred embodiment of the invention is disclosed.

In the drawings,

FIGURE 1 is a top view, partly in section, of a combination lock which is provided with the attack resisting means of present invention, the lock being mounted to a safe door, showing the arrangement of :the respective elements in the lock case;

FGURE 2 is a View of the case with the cover plate removed, showing the bolt in the extended or locked position;

FIGURE 3 is a view of the cover plate subassembly;

FIGURE 4 is a sectional view taken on line 4-4 of FIGURE 2 showing the manner in which the bolt is coupled to the angle bar;

FIGURE 5 is a fragmentary sectional view taken on line 5-5 of FIGURE 2, showing the plunger in depressed condition; and

FIGURE 6 is a fragmentary view similar to FlGURE 5, showing the plunger and depressor after the thermal block has been melted.

In FIGURE l, a combination lock incorporating the principles of this invention is shown mounted on a safe ICC iii

door denoted generally by 1. A dial 2 for setting the combination and operating the lock is located on the outside 3 of the door. The dial is rotatably connected through the sate door by an arbor 4 to the lock assembly proper, which is denoted generally at 5 and is mounted on the inside d oi' the door.

The dial Z is journalled in a fixed frame 7 provided with an index mark ii. A series of numbers is embossed around the circumference of the dial in the usual manner.

The invention particularly relates to the lock assembly 5 mounted on the inside of the door. This assembly is enclosed within a generally rectangular housing comprising a hollow case 9 and a cover plate 10. Certain of the lock elements are mounted from the case while other cooperating elements are mounted on the cover plate, as will be more fully described.

The case 9 is mounted on the safe door 1 by machine screws il accessible only from the interior of the case. The cover plate lil is secured to the case by machine screws (not shown) which pass through openings 12 in the cover plate and are threaded into the case at i3.

The drive shaft or arbor 4 is positively connected to the dial and is journalled in the frame 7', extending through an opening le in the safe door and into the interior of the case. The arbor is externally threaded as at 15 and is provided with a pair of diametrically opposite longitudinal keyways i6 at the end which extends into the case.

A driver l7, which may be conventional, is threaded on the arbor in the interior of the case and its bore is equipped with keyways i9 which match the keyways 16.

The driver comprises a hollow cylindrical shaft i8 and a shoulder Ztl of large diameter which is adjacent the rear Wall 2l ot the case. The circumference of the shoulder 2d is congurated with a notch 28 and a drive dog 30 extends outwardly from the forward face of shoulder 2,9 near its periphery. The driver i7 is positively keyed to the yarbor fi, onto which it is threaded for axial adjustment, by means of the two-pronged key '32. When the Idial is turned and the arbor rotated, the driver is thus positively rotated with it.

The bolt 37 of the lock is a generally rectangular bar which is longitudinally movable in slots .38 and 40 respectively presented by two corner blocks 4l and 42 formed integrally with the case. When the bolt is in the position shown in FIGURE 2 in which it extends outwardly through an opening in the case wall, its outer end engages a cooperating slot in the safe frame, not shown, whereby the safe door is locked. Withdrawal of the bolt inside the case permits the door to be opened. The bolt freely slidable in slots 3S and 4@ so that it may readily be drawn in when the proper combination has been set. The two corner blocks il and 42 and the slots milled in them are shown in section in FIGURE 4.

The lower corner block 4l contains a bore 43 directed perpendicularly to slot 38 and spaced adjacent the slot, preferably below it. A second bore 44 of larger diameter than bore 43 and concentric with its extends into slot 33 from the rear of the case. The upper segment of large bore 4riopens onto slot 38, while smaller bore i3 runs below the slot. A plunger i5 of diameter corresponding to that of bore 44 and having a tip portion 46 of diameter corresponding to that of bore 43 resides in bores 4liand d3, as indicated in FIGURE 5. This plunger is freely movable in axial directions in the bores. A leaf spring i7 secured by screw 48 in recess Sil' at the rear of the case urges the plunger forwardly toward the position shown in FlGURE 6, in which plunger 45 abuts the end of large bore 44. In this position the plunger extends into slot 3d, thereby blocking the slot and engaging cutout 5l in the bolt, as described below. At the same n.2 time, the elongated tip 46 extends approximately to the front surface ot corner block 41.

The lower edge of the bolt which moves in slot Si? is provided with a semi-circular cutout Sil or diameter and location such that when the bolt is in its extended or locked position, the cutout 51 registers with the plunger 45. Under the influence of leaf spring 47 the plunger is yieldably urged outwardly so that it tends to pin the bolt in extended position against longitudinal movement.

The upper bolt slot it? is provided with a detent spring 52 which is fastened to the case at one end by means of a screw 53. This spring, bearing against the inner end of the bolt, tends to throw the bolt outwardly from a partially extended position into its most extended position, in which the plunger is in registry with cutout 51 in the bottom edge of the bolt.

Movement of the boit in slots 3B and is governed by angle bar generally designated by 54, which connects the inner end ot the bolt to the driver 17 once the proper combination has been set, so that an angular rotation of the driver is transformed into a linear movement of the bolt. The angle bar is best pictured in FIGURES l, 2 and 4. At one end, the angle bar is provided with a clevis S, to straddle the bolt. The clevis is pivotally connected to the bolt by a stud 55.

Shank 56 of the angle bar 554 extends diagonally from the bolt to the upper part of the case, above the driver. At its other end, the angle bar has a downwardly extending dog 57 for engagement in the notch 2S with the driver. A fence S extends laterally from the angle bar adjacent the dog and is so arranged that when the dog 57 engages notch 28, the fence engages the aligned gates. A tension spring di? is connected from a post 61 presented by the case to a point 62 on the shank 56 of the angle bar so that the bar is constantly urged downwardly (counter-clockwise in FIGURE, 2), whereby dog 57 rides on the periphery of shoulder 2t?.

Extending into the interior of the case from the plate 1li in axial alignment with arbor d is a hollow cylindrical bearing 74. When the cover plate is mounted on the case, this bearing 74 encircles the outer portion of arbor 4 and driver shaft 18.

Rotatably journalled on bearmg 74 are the lock tumblers, four in the embodiment shown, numbered 78, 79, Si? and 81. These tumblers may be conventional, each having a peripheral gate 93, and need not be described in detail herein.

A boss 103 on the cover plate is provided with a bore 104 (see FIGURES 5 and 6) at a location corresponding to the bore 43 in the case. Into bore 1M is tightly tted a hollow cylindrical thermal plug M5. This is described in detail in relation to its function at a later point. Threaded into the interior of the thermal plug S is a plunger depressor 106. The depressor is provided with a tip 107 of narrow diameter which is engageable with the bore 43 in corner block. The length of the tip is such that when the cover plate is secured to the case, the tip extends into bore 43 and depress/es plunger i5 against the action of leaf spring 47 so that the plunger is clear of slot 3S and cutout 51, whereby the bolt can freely move back and forth in response to motion of the angle bar.

Thermal plug 105, in which the plunger depressor No is set, is made of a low melting point alloy such as Woods metal or the like, having a low melting point.

When the combination has been properly set and the tumbler gates 93 are aligned, the dog 57 of the angle bar will engage the notch 28 in the driver. As the driver 17 is then turned, the dog 57 will be pulled (to the left in FIGURE 2) with it, drawing in the bolt 37. ri`he bolt is permitted to slide in slots 38 and 4i) since the plunger depressor 106 urges the plunger 45 rearwardly in bore 44, out of slot 3S, and disengages the bolt cutout 51.

If any substantial amount of heat is applied to the lock in an attempt to open it, the thermal plug melts before any of the other parts of the lock are allected. As the plug melts, it ceases to support the depressor 1% against the action ot leaf spring d? bearing against plunger 45 so that the spring urges the plunger toward the cover plate in bore lid. This action pushes the depressor into bore lila. The bolt bein.'7 extended, cutout 51 in the bolt is aligned with the plunger, and the plunger is moved by the spring into slot whereby it pins the bolt in the extended position. Once the bolt is pinned, no matter what is done to the lock short ot physically removing it, the sate cannot be opened.

Preferably, the thermal plug should be made of a material which melts at, say, less than 200.

The plunger 45 is normally restrained from pinning the bolt in extended position by the counter force of the plunger depressor ille. It will be seen that it the cover plate be removed or somehow knocked away from the case when the bolt is in the extended position, the plunger will automatically pin the bolt so that the sate cannot be opened. It the cover plate is knocked away, as for example, ir the arbor is drilled or pulled out or driven in, thereby removing the cover plate and tumbler assembly, the safe is thus permanently locked.

When extended, the bolt is precisely positioned by detent spring 52 so that the plunger 45 is aligned with the receptor cutout 51 in the bolt. As the bolt is extended bythe action ofthe driver on the dog 57, the bolt is thrown to a position in which the cutout and plunger are in registry so that the bolt is automatically and consistently positioned for pinning, should either the thermal plug melt or the cover plate be removed.

The foregoing example of a combination lock embodying the principles ot my invention has been by way or illustration and not limitation. It will be apparent from the description that the invention can be modified from the example given to include other variations falling within the scope of the claims which follow:

Having described my invention, I claim:

l. in a lock having a lock case, a cover member securable to said lock case, and a bolt slidable between lock and unlock positions in respect to said case, the improvement comprising, a plunger, means presented by said case adjacent said bolt for mounting said plunger so as to be slidable toward and away from said bolt, plunger receiving means in said bolt aligning with said plunger only when said bolt is in lock position, a spring urging said plunger toward engagement with said plunger receiving means to pin said bolt against movement from said lock position, a plunger depressor, a plunger depressor mounting member having a relatively low melting point positioning said plunger depressor on said cover member to positively hold said plunger out of engagement with said plunger receiving means, said mounting member being meltable under the iniluence of heat to release said plunger and thereby hold said bolt against movement from locked position, said plunger also being released to move into engagement with said plunger receiving means if said cover member is removed from said lock when said bolt is in said lock position.

2. The improvement of claim l wherein said plunger depressor mounting member is a plug received by said cover member, said plunger depressor being mounted in said plug whereby said plunger depressor mounting member yields to said spring when said plug is melted to pin said bolt in said lock position.

3. The improvement of claim 1 wherein a spring urges said bolt toward said lock position whereby said plunger and said plunger receiving means are aligned.

4. in a lock having a lock case, a cover member securable to said case, and a bolt slidable between lock and unlock positions with respect to said case, the improvement comprising a bore in said lock case extending perpendicularly to said bolt and said cover plate, a plunger slidably received in said bore, said bolt having an opening aligning with said plunger when the bolt is in said lock position, a spring urging said plunger into movement restraining engagement with the opening in said bolt, and plunger depressor means on said cover member for holding said plunger out of movement restraining engagement with said bolt, said plunger depressor means being meltable at a relatively low temperature, whereby upon the melting of said plunger depressor means, said plunger is released to restrain movement of said bolt independently of removal of said cover member, and further whereby said plunger is released to restrain movement of said bolt if said cover member is removed from said case when said bolt is in said lock position.

5. In a lock having a lock case, and a bolt slidable between lock and unlock positions with respect to said case, the improvement comprising a bore in said lock case extending perpendicularly to said bolt, a plunger slidably received in said bore, an opening in said bolt aligning with said plunger when the bolt is in said lock position, a spring urging said plunger into pinning engagement with the opening in said bolt, and plunger depressor means normally positively holding said plunger out of pinning engagement with said bolt, said plunger depressor means being meltable at a relatively low temperature, whereby the application of any substantial amount of heat to said lock causes said plunger depressor means to melt and to cease to hold said plunger out of pinning engagement with said bolt.

6. In a lock having a case member, a cover member for said case member, and a bolt slidable between lock and unlock positions with respect to said case member, the improvement comprising, a bore in one of said members, said bore extending toward said bolt and the other of said members, a plunger slidably received in said bore, said bolt having an opening aligning with said plunger when the bolt is in said lock position, a spring urging said plunger into movement restraining engagement with the opening in said bolt, and plunger depressor means on the other of said members for holding said plunger out of movement restraining engagement with said bolt, said plunger depressor means being meltable at a relatively low temperature, whereby upon the melting of said plunger depressor means, said plunger is released to restrain movement of said bolt, and further whereby said plunger is released if said cover member is removed from said case member.

References Cited in the file of this patent UNITED STATES PATENTS 758,394 Szucs Apr. 26, 1904 1,951,628 Prost Mar. 20, 1934 2,660,873 Bennett et al Dec. l, 1953 2,775,113 Behrens Dec. 25, 1956 2,942,449 White June 28, 1960 FOREIGN PATENTS 166,855 Australia Feb. 8, 1956 

5. IN A LOCK HAVING A LOCK CASE, AND A BOLT SLIDABLE BETWEEN LOCK AND UNLOCK POSITIONS WITH RESPECT TO SAID CASE, THE IMPROVEMENT COMPRISING A BORE IN SAID LOCK CASE EXTENDING PERPENDICULARLY TO SAID BOLT, A PLUNGER SLIDABLY RECEIVED IN SAID BORE, AN OPENING IN SAID BOLT ALIGNING WITH SAID PLUNGER WHEN THE BOLT IS IN SAID LOCK POSITION, A SPRING URGING SAID PLUNGER INTO PINNING ENGAGEMENT WITH THE OPENING IN SAID BOLT, AND PLUNGER DEPRESSOR MEANS NORMALLY POSITIVELY HOLDING SAID PLUNGER OUT OF PINNING ENGAGEMENT WITH SAID BOLT, SAID PLUNGER DEPRESSOR MEANS BEING MELTABLE AT A RELATIVELY LOW TEMPERATURE, WHEREBY THE APPLICATION OF ANY SUBSTANTIAL AMOUNT OF HEAT TO SAID LOCK CAUSES SAID PLUNGER DEPRESSOR MEANS TO MELT AND TO CEASE TO HOLD SAID PLUNGER OUT OF PINNING ENGAGEMENT WITH SAID BOLT. 